ROW_NUMBER()

The ROW_NUMBER() is a window function that assigns a sequential integer to each row within the partition of a result set. The row number starts with 1 for the first row in each partition.

SELECT 
   ROW_NUMBER() OVER (
	ORDER BY first_name
   ) row_num,
   first_name, 
   last_name, 
   city
FROM 
   sales.customers;